Sprinkle the lemon juice and salt over the meat. Mix the onion, garlic and chili together well. Heat the ghee in a heavy saucepan over medium heat and fry the onion mixture for 2 minutes. Add the coriander, cumin, turmeric, ginger and pepper, stir well and cook another 2-3 minutes. Add the beef and lemon juice; stir well to coat the meat with the spices. Cook 5-10 minutes. Stir in the tomato paste and beef stock, bring to a boil then cover and simmer gently 30-40 minutes until the meat begins to get tender. Sprinkle in the garam masala and cook for a further 10 minutes. The gravy should by this stage be very thick, if it is not remove the lid from the pan and increase the heat to boil off excess moisture until the gravy thickens.